The present invention relates to electric machines and, more particularly, to an electric machine having a rotor with axially extending conductor bars and an end ring providing electrical communication between the conductor bars.
Induction motors are a common type of electric machine which utilizes a rotor with conductor bars and an end ring that provides electrical communication between the conductor bars. In operation, an AC current is supplied to the stator windings of the induction motor to produce a rotating magnetic field. The rotating electromagnetic field of the stator windings induces electrical currents in the axially extending conductor bars of the rotor. The induced current of the rotor also generates a rotating magnetic field that interacts with the rotating magnetic field of the stator windings to thereby forcibly rotate the rotor. The magnetic field induced in the rotor does not rotate at the same speed as the magnetic field generated by the stator windings, and as a result, such induction motors are also referred to as asynchronous motors. Induction motors have found wide acceptance in a broad range of applications.
An electric machine having the same general construction as an induction motor can also be operated as an induction generator to convert a mechanical torque applied to the rotor to electrical power. By rotating the rotor at a speed faster than the synchronous frequency, a typical induction motor can be operated as an induction generator. Wind turbines oftentimes use induction generators to convert a torque into electrical power. The general operating principles of induction motors and induction generators are well-known to those having ordinary skill in the art.
Induction motors and generators typically have a generally rugged and robust construction due to their relatively simple design which does not require brushes or commutators to provide electrical communication to the rotor. One feature of such electrical machines which is frequently subject to failure, however, is the electrically conductive end ring which provides electrical communication between the axially extending conductor bars of the rotor. Such end rings are often cast of an electrically conductive material such as copper and when the rotor experiences a high rotational speed, such end rings have been known to fail due to the high centripetal forces acting on the end ring. An improved electrical machine which can be employed as an induction motor or generator and has a robust end ring is desirable.